Recently, the progressive scan video format has gained increasing popularity in television broadcasting as well as consumer electronic industries, especially for the proposed 525 progressive (525p) format system. The 525p format system approximately doubles the vertical resolution of the NTSC signal and may be made compatible with the existing 525 interlaced (525i) format system. The 525p format system also provides a near high-definition (HD) picture quality with only a fraction of the transmission bandwidth needed by a high-definition television (HDTV) signal. One example of such a near HD quality video signal is the video signal generated from a progressively scanned film material with 525 vertical scan lines.
A telecine system is commonly used for transferring motion picture film to magnetic recording medium. One such telecine system is a Frame Interline Transfer (Fri) CCD film scanner. Other examples of film-to-tape transfer systems are described in HDTV Advanced Television for the 1990s by Benson and Fink (1991), which is herein incorporated by reference (see Chapter 13). The video signals produced by most telecine systems are interlaced in order to be compatible with the existing interlaced video equipment (though they are capable of generating progressive ones). Once the video signal is in interlaced format, the vertical resolution of the signal is reduced to half of that of the progressive video format. Although there are ways to up-convert an interlaced video signal (IVS) to a progressive video signal (PVS), the conversion equipment is often expensive and the quality is not nearly as good as that of the original progressive counterpart.
FIG. 12 is a block diagram of a typical telecine system for producing a progressive video signal from a motion picture film and for converting the progressive video signal to an interlaced video signal. The system includes the continuous projector 2, a CCD camera 3, and a digital standards converter 4. The system(1) scans a 24-frame-per-second motion picture film through a continuous projector 2 to generate a progressive video signal at the same frame rate; (2) temporarily stores each frame in a digital memory; and (3) retrieves the signal from the memory at a 60-field-per-second rate (in NTSC) through a digital standards converter 4 which performs a 2:1 vertical scan line decimation (e.g., scan line averaging) and a 3-2 pull down operation on the resultant even and odd fields. It is necessary for the converter 4 to perform an averaging process, commonly referred to as field integration, to reduce interline flicker in an interlaced scan monitor. The interlaced video signal is recorded on a magnetic tape or on an optical disk for playback through a playback device 6, such as a VTR, on a display device 8.
FIG. 11 illustrates the aperture responses of an interlaced film scan system where the image signal has been down-converted to interlaced format as described above and a hypothesized progressive film scan system where the motion picture film is progressively scanned without field integration (i.e., 2:1 vertical decimation). The graph compares aperture response against the Nyquist limit. The graph demonstrates that there is a significant loss of the vertical frequency content in the interlaced film scan system shown by the dashed line as compared to the progressive film scan system shown by the solid line.
There have been attempts to improve vertical resolution of video signals derived from motion picture film. U.S. Pat. No. 5,485,280 entitled APPARATUS AND METHOD FOR PRODUCING DOWNWARDS COMPATIBLE VIDEO SIGNALS WITH INCREASED VERTICAL RESOLUTION, AND APPARATUS FOR REPRODUCING AND DISPLAYING SAME issued on Jan. 16, 1996 and by Fujinami, and U.S. Pat. No. 5,510,902 entitled APPARATUS AND METHOD FOR PRODUCING DOWNWARDS COMPATIBLE VIDEO SIGNALS WITH INCREASED VERTICAL RESOLUTION, AND APPARATUS FOR REPRODUCING AND DISPLAYING SAME issued on Apr. 23, 1996 and by Fujinami, each disclose a method and apparatus for producing downward compatible video signals with increased vertical resolution, and apparatus for reproducing them. Each of these patents is incorporated herein by reference.
The process described in these patents includes several steps. First, the film is scanned though a high definition telecine apparatus to produce an interlaced high definition video signal with 1125 scanning lines and an aspect ratio of 16:9. The interlaced high definition video signal is converted to a progressive high definition video signal which is then down converted to a standard definition video signal with fewer vertical lines. Finally, the progressive standard definition video signal is converted to an interlaced standard definition video signal with increased vertical resolution. The increased vertical resolution of the resultant interlaced video signal is achieved by directly providing the odd lines of each standard definition progressive frame into an odd field memory corresponding to the interlaced video signal. Similarly, the even lines of each standard definition progressive frame are directly provided to an even field memory. As a result, the vertical resolution of the interlaced video signal is increased with respect to that of a standard NTSC video signal because there is no vertical lowpass filtering during the down conversion.
A flag signal is also provided to a recording/playback device to indicate the presence of the interlaced video signal with increased vertical 5 resolution. Therefore, a progressive scan monitor can be selected to reproduce the intended progressive images. The interlaced video signal with increased vertical resolution cannot, however, be properly displayed in an interlaced scan monitor without interline flicker or significant aliasing effect with or without vertical lowpass filtering. Hence the process proposed in U.S. Pat. No. 5,485,280 and U.S. Pat. No. 5,510,902 is not fully compatible with existing systems. Furthermore, substantial hardware modification to an existing telecine system is needed in order to generate the interlaced video image with increased vertical resolution.
Thus, it is desirable to develop an apparatus for a telecine system such as a FIT-based CCD film scanner to preserve the vertical resolution of the progressive film scan system while maintaining interlaced video signal output for backward compatibility with existing recording equipment and standard video interfaces. It is also desirable to develop an apparatus that converts between progressive video signals and interlaced video signals while preserving the vertical resolution of the progressive video signal and maintaining the same signal bandwidth of the interlaced video. so that both interlaced and progressive video signals are available for different applications. It is also desirable to provide an economic solution to the restoration of the full vertical resolution corresponding to a progressive video from a conventional interlaced video source produced by any CCD based film scanner or other similar device.